1. Field of the Invention
This invention relates to demodulation of an analog signal. More particularly, the present invention relates to the demodulation of the Loran Data Channel (LDC).
2. Description of the Prior Art
Loran (Long Range Navigation) is a terrestrial navigation system composed of chains of low frequency radio transmitters that are used to determine position of receivers. Presently, the U.S. Coast Guard is developing the LDC, also referred to as eLoran, or enhanced Loran. The purpose of eLoran is to supplement the current Loran-C (version C) system with a differential capability that will provide information such as, absolute time, Differential Loran corrections, anomalous propagation (early skywave) warnings, and LDC system information for high-integrity applications. The addition of these capabilities will greatly increase the accuracy and utility of the Loran system. This differential capability is implemented and transmitted using 32-state Pulse Position Modulation technique on an additional Loran pulse (ninth pulse) added in every Group Repetition Interval (GRI.) Therefore, in order to utilize this capability at the receiver end, a method and related system are required to demodulate the received signal and identify the differential message transmitted over the ninth pulse. Such a demodulation would make the differential capability available for subsequent use to increase the accuracy and utility of the Loran system.